1. Field of the Invention
The present invention relates to a method for drying semiconductor substrates.
2. Description of the Prior Art
In the wafer process for preparing semiconductor devices, semiconductor substrates are subjected to a drying treatment at various steps. For example, a semiconductor wafer is dried at a pretreatment step such as the diffusing step. Moreover, a semiconductor wafer having a photo-resist film formed thereon is dried prior to the patterning of the photo-resist film and also after the patterning thereof. It is intended by the drying prior to the patterning thereof and the drying after the patterning thereof that the photo-resist is not only dried but also baked and, therefore, such drying prior to the patterning and that after the patterning are called "pre-baking" and "post-baking", respectively. However, the conventional drying methods adopted at these steps involve various problems to be solved.
For example, for drying at a pretreatment step, such as the diffusing step, there is adopted a method in which semiconductor substrates are maintained at an elevated temperature of from 100.degree. to 150.degree. C. for 10 to about 15 minutes in nitrogen (N.sub.2). In this method, the drying time is long and, therefore, the method involves problems of reduction of clarity in the semiconductor substrates. Furthermore, for drying semiconductor substrates before coating thereof with a photoresist in a photo-process, especially semiconductor substrates having an insulating glass layer of a high moisture-absorbing property attached to the surface thereof, in order to improve the adhesion between the semiconductor substrate and the photo-resist film, it is necessary to carry out a heat treatment in nitrogen at about 200.degree. C. for about 30 minutes by using an electric furnace or the like. Moreover, in the conventional drying method using a heating furnace, which is adopted for performing the drying treatment of semiconductor substrates having a photo-resist film attached thereto in the photo-process, since the photo-resist film is dried from the surface thereof, in order to remove a solvent contained in the photo-resist film completely, it is necessary to use an electric furnace and maintain the semiconductor substrate in nitrogen at about 150.degree. C. for about 15 or 20 minutes. Therefore, during this drying treatment, the surface of the photo-resist film deteriorates, and various disadvantages arise. For example, the photo-resist film becomes unsuitable for formation of a delicate and fine pattern thereon and peeling of the photo-resist film becomes difficult.
Japanese Laid-open Patent Application No. S50-69,972/1975 discloses an apparatus for heating a semiconductor wafer by microwave heating wherein the wafer is irradiated with microwaves in such a state that the predominant faces thereof are parallel to the opening face of a waveguide provided therein. This apparatus is provided with means for rocking the wafer so that the wafer is heated uniformly. However, the apparatus provided with such rocking means is complicated and the production of the semiconductor element is not efficient.